Cobalt-base alloy



United States Patent 3,241,954 COBALT-BASE ALLOY Rudolf H. Thielernann, Portland, 0reg., assignor to Martin Metals Company, a corporation of Delaware No Drawing. Filed Aug. 29, 1963, Ser. No. 305,514 3 Claims. (Ci. 75-171) This is a continuation-in-part of application Serial No. 751,149 filed July 28, 1958, now abandoned which in turn was a continuationdn-part of application Serial No. 683,457, filed September 12, 1957, now abandoned.

This invention relates to cobalt-base casting alloys which include alloying metal additives which make the resulting alloy corrosion resistant and of high strength at elevated temperatures. More particularly, it relates to cobalt-base alloys containing tantalum and having improved rupture life and oxidation resistance at elevated temperatures of the order of 1800 F. to 2200 F.

In accordance with the present invention, alloys are prepared which comprise a cobalt-base alloy containing tungsten, tantalum and boron in proportions and in relationship, one to the other, necessary to attain the properties at high temperatures of resistance to oxidation and rupture life which properties are superior to those exhibited by commercially available cobalt-base alloys at 1600 F. to 1750 F.

The alloy of this invention is useful as the material of manufacture of turbine blades, vanes and other parts of gas turbine engines for exhaust valves and manifolds for internal combustion engines, in high temperature heat exchangers and as linings for retorts and container vessels used in the chemical and metallurgical industries, or as an oxidation resistant coating material for metals and metal alloys such as columbium, molybdenum, cobalt base alloys, etc., Whose resistance to oxidation at elevated temperatures is inadequate.

If the alloys are to function properly, for example, as turbine blades or related parts of jet engines, they must maintain high strength at elevated temperatures, particularly in oxidizing atmospheres encountered in the operation of engines. Cobalt-base metal alloys and particularly those incorporating molybdenum, vanadium, etc. which have been known heretofore for use, for example, as turbine blades, etc. have placed limitations upon the maximum temperature safely usable in the combustion zone not because of lack of strength initially but because of rapid deterioration due to corrosion and oxidation at higher temperatures which oxidation results in loss of load carrying ability in the oxygen penetrated portion of the structural member.

Restriction of the combustion chamber temperatures to relatively low operating temperatures in order to provide adequate margin of safety, seriously limits the performance of turbine engines. The ability of the alloys of this invention to operate safely as structural members of turbine engines in an oxidizing atmosphere at temperatures of 1800 F. to 2200 F. permits markedly improved performance since, at high temperatures, the total thrust of a gas turbine engine increases and the amount of fuel consumed per pound of thrust decreases.

Basically, the metal alloy of this invention is comprised by weight of: from about 15% to about 30% of chromium; from about 5% to about 15% of tungsten; from about 4% to about 16% of tantalum; from about 0.01% to 0.2% of boron, from about 0.1% to about 1.3% of carbon and from about 40% to about 70% of cobalt.

Chromium is incorporated in this composition for the purpose of improving strength and oxidation resistance. The higher quantities of chromium within the above specified range improve oxidation resistance but the deleterious embrittling effect of the larger amounts of chromium tend to become apparent. Preferably, chromium is used in quantities in the range between about 16% and about 25%.

In the alloy of this invention, tantalum and columbium are not equivalent. If columbium is "substituted for tantalum in the alloy of this invention either on a weight basis or an atomic equivalent weight basis, the resulting alloy does not possess the same high temperature corrosion resistance characteristic of the alloy of this invention. This does not mean that minor amounts of columbium cannot be present in the alloy, provided the amount of columbium is not more than half of the amount of tantalum in the alloy. Preferably the amount of columbium should not exceed about 2% when the tantalum content of the alloy is less than 7% and not exceed about 2.5% when the tantalum content is greater than 7%.

While molybdenum is not a primary constituent of the alloy of this invention, I have found that the properties of the alloy of this invention are not deleteriously affected if the alloy includes an amount of molybdenum which is not more than one half the amount of tungsten in the alloy, and, in any event, is no greater than 3.5% of the weight of the alloy.

It has been further found that the inclusion of any one or more of the following ingredients: up to about 1.5% of silicon, and up to about 3.5% of nickel and/ or iron may in certain formulations improve various metallurgical characteristics of the alloy. Preferably the nickel and iron content of the alloys is less than 2.5%.

To achieve the optimum desired properties, it is preferred that the following impurities which may be in the alloy be held to the following limits, by weight. The manganese content in the final alloy should be no more than about 2%; the interstitial elements such as nitrogen, hydrogen, tin, =lead, and the like, should be kept as low as possible. In addition, no more than about .5 total of deoxidizers such as calcium, magnesium, or the like, should be present in the final alloy.

A preferred range of proportions of the constituents of the alloy of this invention which has an especially high oxidation resistance at temperatures of about 2000 F. and above, is as follows: from about 16% to about 25% of chromium; from about 7.5% to about 12.5% of tungsten; from about 7% to about 11% of tantalum; from about 0.6% to about 1.0% of carbon; from about 0.01% to about 0.2% of boron; and from about 50% to abou 62% of cobalt.

The following are examples of the proportions and test results of the cobalt-base metal alloy of this invention.

Example I An alloy melt of a cobalt base alloy composition containing about 20% of chromium, about 10% of tungsten, about 4% of tantalum, about 0.1% of boron, about 0.45% of carbon, and the balance, essentially cobalt, all by weight, Was prepared by melting a chromium-cobalt mix in a magnesia crucible under high vacuum conditions, following which the tungsten, tantalum, boron and carbon in the form of graphite were added. A cluster of six test bars were formed from the melted alloy by the usual investment casting technique under high vacuum conditions. These bars were each 3" long and A" in diameter. The test bars of the above composition had an elongation of 6% at a room temperature under a tensile stress of 100,000 p.s.i.

The test bars of the above composition had a rupture life in excess of 90 hours under a load of 20,000 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of hours under a load of 15,000 p.s.i. at a temperature of 1700 F. in air.

3 Example 11 A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 25% of chromium, about of tungsten, about 10% of tantalum, about 0.01% of boron, about 0.85% of carbon, about 0.5% of silicon, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 0.84% at room temperature under a tensile stress of 150,000 p.s.i.

The test bars of this example had a rupture life in excess of 44 hours under a load of 17,000 p.s.i. at a temperature of about 1800 F. in air and a rupture life in excess of 42 hours under a load of 8,000 p.s.i. at a temperature of about 2000 F. in air.

The oxidation penetration was nil after 100 hours at 2000 F. in moving air and also after 24 hours at 2100 F. in moving air.

Example III A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about of chromium, about 10% of tungsten, about 10% of tantalum, about 0.01% of boron, about 0.85% of carbon, about 0.5% of silicon, about 5% of iron, and the balance, essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 0.8% at room temperature under a tensile stress of 122,000 p.s.i.

The test bars of this example had a rupture life in excess of 7.5 hours under a load of 17,000 p.s.i. at a temperature of about 1800 F. in air and a rupture life in excess of 7 hours under a load of 8,000 p.s.i. at a temperature of about 2000 F. in air. The oxidation penetration was nil after 100 hours at 2000 F. in moving air and 0.22 mils per side per hour after 24 hours at 2100 F. in moving air.

Example IV A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 25% of chromium, about 10% of tungsten, about 10% of tantalum, about 0.01% of boron, about 0.85% of carbon, about 0.5% of silicon, about 5% of nickel, and the balance, essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 1.6% at room temperature under a tensile stress of 143,400 p.s.i.

The test bars of this example had a rupture life in excess of 17 hours under a load of 17,000 p.s.i. at a temperature of about 1800 F. in air and a rupture life in excess of 19 hours under a load of 8,000 p.s.i. at a temperature of about 2000 F. in air. The oxidation penetration was nil after 100 hours at 2000 F. in moving air, and was 0.02 mils per side per hour after 24 hours at 2100 F. in moving air.

Example V A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 20% of chromium, about 10% of tungsten, about 10% of tantalum, about 0.2% of boron, about 1.3% of carbon, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 1% at room temperature under a tensile stress of 145,000 p.s.i.

The test bars of this example had a rupture life in excess of 50 hours under a load of 25,000 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 45 hours under a load of 22,000 p.s.i. at a temperature of about 1700 F. in air.

Example VI A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 20% of chromium, about 10% of tungsten, about 10% of tantalum, about 0.2% of boron, about 0.8% of carbon, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 3% at room temperature under a tensile stress of 134,000 p.s.i.

The test bars of this example had a rupture life in excess of hours under a load of 25,000 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 73 hours under a load of 20,000 p.s.i. at a temperature of about 1700 F. in air.

Example VII A 5 pound alloy melt and test bars of the same dimensions as set forth in Example -I of a cobalt base metal alloy composition containing about 20% of chromium, about 10% of tungsten, about 10% of tantalum, about 0.1% of boron, about 0.65% of carbon, and the balance, essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 3% at room temperature under a tensile stress of 120,000 p.s.i.

The test bars of this example had a rupture life in excess of 70 hours under a load of 25,000 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 65 hours under a load of 20,000 p.s.i. at a temperature of about 1700 F. in air.

Example VIII A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 28% of chromium, about 5% of tungsten, about 8% of tantalum, about 0.2% of boron, about 0.7% of carbon, about 2.5% of molybde= num, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 0.8% at room temperature under a tensile stress of 108,- 000 p.s.i.

The test bars of this example had a rupture life in excess of 100 hours under a load of 20,000 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 100 hours under a load of 15,000 p.s.i. at a temperature of about 1700 F. in air.

Example IX A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 22% of chromium, about 8% of tungsten, about 8% of tantalum, about 0.2% of boron, about 0.7% of carbon, about 0.2% of silicon, about 1.0% of nickel, about 1.0% of iron, about 2.5% of molybdenum, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 2% at room temperature under a tensile stress of 118,000 p.s.i.

The test bars of this example had a rupture life in excess of 100 hours under a load of 20,000 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of hours under a load of 115,000 p.s.i. at a tem perature of about 1700 F. in air.

Example X A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 20% of chromium, about of tungsten, about 9% of tantalum, about 1% of columbium, about 0.1% of boron, about 0.65% of carbon, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 3% at room temperature under a tensile stress of 118,000 p.s.i.

The test bars of this example had a rupture life in excess of 70 hours under a load of 25,000 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 65 hours under a load of 20,000 p.s.i. at a temperature of about 1700 F. in air.

Example XI A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 23% of chromium, about 9% of tungsten, about 8% of tantalum, about .05% of boron, about .90% of carbon, about 2.5% of iron, about 1.0% of columbium, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had a rupture life of approximately 7'6.3 hours under a load of 17,000 p.s.i. at a temperature of about 1800 F. in air and a rupture life of approximately 40.8 hours under a load of 5,000 p.s.i. at a temperature of about 2000 F. in air.

Example XII A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about of chromium, about 15% of tungsten, about 13% of tantalum, about 0.2% of boron, about 0.65% of carbon, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 2% at room temperature under a tensile stress of 115,- 000 p.s.i.

The test bars of this example had a rupture life in excess of 100 hours under a load of 20,000 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 100 hours under a load of 15,000 p.s.i. at a temperature of about 1700 F. in air.

Example XIII A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about of chromium, about 10% of tungsten, about 12% of tantalum, about 0.2% of boron, about 0.6% of carbon, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 4% at room temperature under a tensile stress of 115,000 p.s.i.

The test bars of this example had a rupture life in excess of 100 hours under a load of 20,000 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 90 hours under a load of 15,000 p.s.i. at a temperature of about 1700 F. in air.

Example XIV A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 22% of chromium, about 10% of tungsten, about 10% of tantalum, about 1% of carbon, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 14.1% and a rupture life in excess of 83.5 hours under a load of 22,500 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 52. 1 hours under a load of 17,000 p.s.i. at a temperature of about 1800 F. in air.

Example XV A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 22% of chromium, about 10% of tungsten, about 10% of tantalum, about .05% of boron, about 1% of carbon, and the balance essentially cobalt, all by Weight, Were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 18.5% and a rupture life in excess of 299.4 hours under a load of 22,500 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 93.8 hours under a load of 17,000 p.s.i. at a temperature of about 1800" F. in air.

Example XVI A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 22% of chromium, about 10% of tungsten, about 10% of tantalum, about .10% of boron, about 1% of carbon, and the balance essentially cobalt, all by Weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an elongation of 25.8% and a rupture life in excess of 270.7 hours under a load of 22,500 p.s.i. at a temperature of about 1600 F. in air and a rupture life in excess of 47.9 hours under a load of 17,000 p.s.i. at a temperature of about 1800 F. in air.

Example XVII A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 25% of chromium, about 10% of tungsten, about 4% of tantalum, about .01% of boron, about .85% of carbon, about .5% of silicon, about 2% of columbium, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an average specific weight gain (mg/cm?) of 9.45 and an average maximum depth of penetration of 0.0005 inch when exposed to air for a period of 72 hours while being maintained at a temperature of 2000 F.

Example XVIII A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 25% of chromium, .01% of boron, about of carbon, about .5% of about 10% of tungsten, about 7.75% of tantalum, about silicon, about .5% of columbium, and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had an average specific weight gain (mg/cm?) of 3.2 and an average maximum depth of penetration of 0.0025 inch when exposed to air for a period of 72 hours while being maintained at a temperature of 2000 F.

Example XIX A 5 pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 25% of chromium, about 12.5% of tungsten, about 5% of tantalum, about 0.5% of boron, about 1.20% of carbon, about 3.5% of iron, about 2% of colum-bium and the balance essentially cobalt, all by weight, were prepared in the same man ner as set forth in Example I.

The test bars of the example had an elongation of 5.8% and a rupture life in excess of 98.1 hours under a load of 17,000 p.s.i at a temperature of about 1800" F. in air.

Example XX A pound alloy melt and test bars of the same dimensions as set forth in Example I of a cobalt base metal alloy composition containing about 25% of chromium, about of tungsten, about 10% of tantalum, about 0.01% of boron, about 3% of nickel and the balance essentially cobalt, all by weight, were prepared in the same manner as set forth in Example I.

The test bars of this example had a rupture life of 17.4 hours under a load of 17,000 psi at a temperature of 1800 F. in air and an average elongation of about 12.0%.

Comparison of the alloys of Examples XV, IV and XX shows that decreasing the nickel content from 5% to 2.5%, a reduction of 50%, makes an approximately fourfold (approximately 400%) increase in rupture life. Elimination of nickel entirely produces an alloy with a rupture life of 299.5 hours as compared to 17 hours for alloys containing 5% of nickel, a markedly superior rupture. life. Comparison of the oxidation data for the alloys of Examples IV, XVII and XVIII shows that introduction of 0.5% of columbium into the alloy causes a reduction in the oxidation resistance and introduction of 2.0% of columbium makes a drastic reduction in oxidation resistance, i.e., an approximately 300% increase in oxide formation. Comparison of the strength of the alloys of Examples XV, III and XIX shows that increase in iron content results in a drastic reduction in rupture life.

Although the invention has been described in connection with specific embodiments, it will be understood that these are not to be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

I claim:

1. A :metal alloy consisting essentially of by weight, from about 15% to about of chromium, from about 5% to about 15% of tungsten, from 7% to about 16% of tantalum, up to about 2.5% of columbium, from about 0.01% to about 0.2% of boron, from about 0.01% to about 1.3% of carbon and from about to about of cobalt.

2. A metal alloy consisting essentially of by weight, from about 16% to about 25% of chromium, from about 7.5% to about 12.5% of tungsten, from about 7% to about 11% of tantalum, up to about 2% of columbium, from about 0.6% to about 1% of carbon, from about 0.01% to about 0.2% of boron and from about 50% to about 62% of cobalt.

3. A metal alloy consisting essentially of by weight, from about 16% to about 25% of chromium, from about 7.5% to about 12.5% of tungsten, up to about 3.5% of molybdenum, from about 7% to about 11% of tantalum, up to about 2.5% of columbium, from about 0.6% to about 1% of carbon, from about 0.01% to about 0.2% of boron, up to about 1.5% of silicon, up to about 2.5% of nickel, up to about 2.5% of iron and from about 50% to about 62% of cobalt.

References Cited by the Examiner UNITED STATES PATENTS 2,246,078 6/ 1941 Rohn et a1. 171 2,684,299 7/ 1954 Binder 75171 2,771,360 11/1956 Malcolm 75-171 2,974,037 3/1961 Thielemann 75--l71 3,118,763 l/1964 Thielemann 75171 FOREIGN PATENTS 542,813 6/1957 Canada.

DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner. 

1. A METAL ALLOY CONSISTING ESSENTIALLY OF BY WEIGHT, FROM ABOUT 15% TO ABOUT 30% OF CHROMIUM, FROM ABOUT 5% TO ABOUT 15% OF TUNGSTEN, FROM 7% TO ABOUT 16% OF TANTALUM, UP TO ABOUT 2.5% OF COLUMBIUM, FROM ABOUT 0.01% TO ABOUT 0.2% OF BORON, FROM ABOUT 0.01% TO ABOUT 1.3% OF CARBON AND FROM ABOUT 40% TO ABOUT 70% OF COBALT. 